The present invention relates generally to hydraulically actuated implements attached to agricultural tractors or other primary sources or motive power, and more particularly to systems and methods for controlling the draft load of an implement in such an arrangement.
One of the most common uses of agricultural tractors is to move implements through agricultural fields to cultivate and condition the soil. Implements are commonly connected to the tractor using a three-point hitch or a drawbar. A three-point hitch device typically comprises two bottom lift arms, to which the implement is connected in rotary manner to swing about a given hinge axis; and a top link interposed between the tractor frame and the implement to control the angular position of the implement about the hinge axis. The lift arms are moved by a further actuating cylinder (or cylinders) interposed between the tractor frame and the lift arms, movement of the lift arms raising and lowering the implement with respect to the ground. Three-point hitches may be front or rear mounted. Implements may thus be connected in front of the tractor and pushed through the soil, behind the tractor and pulled through the soil, or both. Similarly most trailed implements towed by a drawbar include one or more wheels pivotably connected to the implement in a manner to raise and lower the implement with respect to the ground offering an another method for altering implement position. Movement of the implement-attached wheels is used to establish implement position with respect to the ground. Three-point hitches and towed implement position control, as well as numerous variations thereof, are well known in the agricultural industry.
The digital controller used for hitch controller 200 and other digital controllers used in the tractor are coupled over the CAN bus 180. Engine control system 161 also includes a digital interface that enables it to communicate over the same CAN bus. The communications bus (CAN bus) 180 is preferably a controller area network bus such as the bus defined in the SAE J1939 standard. Individual communications circuits within the communications bus 180 are preferably Siemens or Motorola brand CAN bus controller circuits that are either integrally formed with the controllers or are coupled to the controllers. By using the existing CAN bus 180, the present invention obtains the sensor information without the need to employ additional, task-specific sensing circuits. These preferences are based upon actual field test results, and reflect choices made thereon. However, it should be obvious that components other than these will work, and certainly improvements by other manufacturers will be made and may prove even more suitable than those specifically identified herein. Additionally, while a serial communications protocol is described, use of other protocols (e.g., parallel) are equally suitable and thus not precluded by this invention.
Electronic draft control systems alleviate the need for manual hitch adjustments by controlling the position of the connected implement in response to loads applied to the tractor by the implement. The control systems allow the depth of engagement to be adjusted so that a near constant draft load is applied to the tractor to smooth tractor operation. Alternatively, control systems may maintain the implement at a near constant depth of engagement thereby allowing the implement tools to follow field contours. Such control systems typically use one or more measuring devices to sense the draft loads applied to the hitch by the implement and then generate a control output to adjust the hitch position in response to the applied loads and desired position. Measuring devices are subjected to generally harsh environments that increase failure rates and reduce reliability. Such force sensing devices are typically installed only on rear three-point hitches which limit the draft control to rear hitched implements.
Key considerations in monitoring implement draft load are the accuracy of the load reading and the time lag between an actual change in the draft load and the recognition of that change by the control system. Sensing devices capable of providing accurate and near-instantaneous measurements of the draft load are expensive, susceptible to electrical noise interference from the tractor and may be limited in their capacity.
Hitch mounted implements are supported by the actuating cylinders used to position three-point hitches. Actuating cylinders must provide an upward force on the hitch to support the implement above the ground. When the implement engages the ground and is towed through a field, a downward force is generated which must be counteracted by the actuating cylinders to maintain the implement at a constant depth of engagement. Measuring the cylinder pressure provides an efficient, near instantaneous method for measuring the downward force created by the implement. Actuating cylinders used to position support wheels in towed implements experience similar loading characteristics and may therefore be similarly used to determine downward loading on the implement.
It would be a great advantage to provide an economical and reliable system for controlling the depth of ground engagement and therefore the draft load imposed on the tractor by the coupled implement in a manner to maintain a constant draft load on the tractor. Further advantages would be realized if the draft load control system would function for any connected implement regardless of whether the implement is connected to a front hitch or a rear hitch. Still further advantages would be realized if the draft load sensing apparatus provided near-instantaneous measurements of the draft load to the control system thereby enabling automated draft control thereby alleviating the operator from manually monitoring and controlling the draft load. Still further advantages would be realized if the draft load control system could accept other parameters, such as engine load, to further refine the draft load control scheme. These and other advantages are provided by the draft control system described below.